Braun tube



A K S U R E BRAUN TUBE Filed Jan. 24, 1935 2 Sheets-$116M. 1

E1. RUSKA BRAUN TUBE Filed Jan. 24, 1935 2 mats-Sheet 2 In Us!) forPatented Oct. 31, 1939 UNITED STATES PATENT OFFICE lin, GermanyApplication January 24, 1935, Serial No. 3,319 In Germany January 26,1934 1 Claim.

This invention relates to an improved Braun tube.

Braun tubes, particularly television and oscillograph tubes, should besensitive to low volt- 5 ages for modulating the ray, but the modulatedimage must nevertheless possess great intensity. This object can beattained by high current density of the ray and great screensensitivity, and an additional expedient which is quite ef- 10 fectiveconsists in increasing the speed of the electrons toward the screenafter the deflecting fields are passed. It is known to provide foracceleration directly before the screen by applying thereto a strongpositive voltage with respect to 15 a fine-meshed Wire nettingpositioned closely in front of it, Furthermore, it is possible to buildup between the deflecting plates and the fluorescent screen a' graduallyrising potential field by a plurality of annular electrodes which may be20 arranged on the inside of the glass bulb on gradually risingpotentials, or by a single spiral electrode subjected to the entirevoltage. The firstmentioned method is open to the objection that part ofthe radiated energy is lost, absorbed by 5 the wire netting, for theproduction of the image and that, owing to the irregularities of theelectric field, distortions of the image points will appear at themeshes. the drawback of involving great difliculties in their technicalapplication.

This invention proposes to eliminate these troubles by employing for theacceleration of the ray electrons to the screen an electric lenscomprising two or more disc electrodes or net shaped 35 electrodes andhaving a higher potential on the screen than on the cathode side. Whileaccelcrating the electrons, this lens reproduces, at a definite focalsurface within the tube, such as the fluorescent screen, the image of avirtual 40 or real primary image, 1. e., of a virtual or real modulatedcross section of an electronic ray at a defined cross section of thetube, so that the brightness of the image on the screen is increased bythe lens according to the rise in po- 45 tential, the modulation of themy being efiected, according to the invention, at low voltage and,correspondingly, at small deflecting voltages and currents.

As in all apparatus of this class the original 50 source of the ray isan electron gun which determines the shape and, proportionally, the sizeof the image point or elementary area appearing on the fluorescentscreen. The modulation of the image point as it is concurrentlyvaried in55 intensity and deflected across the screen is in- Both methods sufierfrom tegrated by the eye to give the appearance of an image. No.actualelectron image of a pictured object ever exists within the tube, but itis convenient to consider the ordered pattern of image points which aresuccessively formed as if 5 they were simultaneous, and to refer to themas an image. It will be apparent that where the proper electric fieldconditions obtain to form a complete and simultaneous image of apictured object these same conditions will necessarily hold forindividual points, and hence no errors are introduced by considering theaggregate of such points as an image.

Corresponding to the virtual or real object, two embodiments of theinvention are illustrated in the accompanying schematic drawing, inwhich Figure 1 shows a tube for forming a virtual primary image of theobject; and Figure 2,

a tube for forming a real primary image, virtual and real having thesame connotations as in optics.

In both instances, either the cathode itself or an irradiated diaphragmacting as electronic source defines an image point, the latterpossibility, besides insuring the desired smallness of the point ofimage affords the advantage of choosing the form of the image point andpermits the use of large-surfaced cathodes which. yield more ,current,such as point-like, say, directly heated horse shoe cathodes, orlarge-sur- 3o faced cathodes such asindirectly heated oxide cathodes.The embodiment shown in Figure 1 employs a cathode-defined image point,while Figure 2 employs a diaphragm-defined image point;

According to Figure 1, the ray transversely modulated, i. e., deflectedat a relatively low electronic speed is accelerated by an electric lensdirectly behind the deflecting plates, The fluorescent screen shows thereal image of a virtual object found by extending the modulated beamback to the plane of the electronic source.

In the embodiment shown in Figure 1, the source of electrons is theconventional horseshoe or hairpin filamentary cathode l, which issurrounded by a cylindrical control electrode 2 for varying theintensity of the electron stream. In front of the cathode an apertureddiaphragm 3 is mounted in a shielding cylinder 4!, to which is applied apotential positive to the cathode. Cathode, control electrode, anddiaphragm combine to form an accelerating electron lens, which acts todecrease the divergence of the electron stream from the cathode as itpasses through the shielding cylinder.

The opposite end of the shield supports a second diaphragm 5, shown asformed with an inwardly flared flange. Opposing the diaphragm I is asecond diaphragm 8. formed with a symmetrically arranged flange, andconnected to and forming part of a second anode I, which lines theflaring portion and a part 01' the neck of the tube. The anode I isoperated at a potential which is highly positive to the first anodestructure comprising diaphragms 3 and I and the cylindrical shield 4. Inother words, the electrons are given most of their acceleration betweenthe diaphragms 5 and 8 which together form a second electron lens, andstrike the flucrescent screen 8 at theend of the tube with this finalhigh velocity to cause a correspondingly brilliant fluorescence thereon.V

The usual pairs 01 electrostatic deflecting plates 9 and III are mountedwithin the shield 4. The pairs of plates are mounted perpendicularly toeach other, and for television use one. pair is excited by the pictureor vertical deflection frequency. while the other pair is excited by theline or horizontal deflection frequency.

In operation, the electron stream as it passes the deflecting plates isweakly divergent and traveling at low velocity, and is hence easilydeflected. The second accelerating lens I, i not only greatly increasesthe velocity but causes the rays to converge, coming to a focus andforming a real image in the plane of the fluorescent screen 8. Thisimage, considered in the aggregate as integrated by the eye, correspondsto a virtual image such as might be formed by a similarly deflected beamin a plane behind the first lens.

In the embodiment shown in Figure 2 an extended-surface, indirectlyheated cathode II is shown with a control electrode l2 formed as anextension of the geometrical surface defining the cathode face. In frontof the cathode is mounted a hollow anode ll, apertured to permitelectrons from the cathodes to enter and reach a diaphragm ll and toirradiate the small aperture formed therein with relatively highvelocity electrons, the accelerating potential applied to the anodebeing comparatively high. In this manher a relatively large electronflow may be obtained through an exceedingly small aperture of anydesired shape. The forward end 01' the anode shield is closed by adiaphragm l5 which is provided with an inwardly flaring flange and whichforms the first element of an electron lens.

The second element of this lens is the diaphragm l6 which is mounted ina cylindrical tion.

tional, its purpose merely being to define the image field.

The diaphragm 20, opposed to the diaphragm area may be very small ascompared to the size oi the final image and hence little power will beneeded to deflect the electron stream at the low velocity which itpossesses as it passes between the deflecting plates. The primarydifierence between this embodiment and the first embodiment is that theprimary aggregate image is a real image iormed ahead or the first lensinstead of a virtual one formed behind it.

It will be understood that the two embodiments shown in the drawings byno means exhaust the possibilities of the structures by which thisinvention may be carried out. The type 0! cathode shown in Figure 2 maybeused with the virtual-image type of apparatus, and vice versa.

Where the virtual-image system is used, the flrst pair of deflectingplates may be placed on one side oi! the first lens and the second pairof plates on the opposite side. Furthermore, the particular type of lensdisclosed is only one form of several which are well known in thescience of electron optics, and any of these types of lenses may be usedin. the practice of the inven- With the lenses at the command oi thedesigner, the actual combinations which may be used are almostunlimited. In the examples shown, the first lens in Figure 1, where theprimary image is virtual, is an accelerating lens, whereas the firstlens in Figure 2 is a retarding lens; if proper regard is had to thevarious velocities involved these conditions maybe reversed. With suchpossibilities in mind, what I claim as new is the invention as expressedby the iollowng claim.

I claim:

In a Braun tube, a source oi electrons, a tubu- Lar: shield positionedin the path of electrons emitted by said source, an apertured diaphragmpositioned at each end of said tubular shield, each of said diaphragmsbeing formed and positioned to form one element of an electron lens,means within the shield for deflecting electrons passing therethrough, afluorescent screen positioned to receive electrons passing through saidshield, and additional electron lens elements mounted adjacent saiddiaphragms without said shield and cooperating with said diaphragms toform a real image of successive points as the beam is deflected in theplane of said screen, and to form an additional primary image behind thecloser of said diaphragms as viewed from said screen.

ERNST RUSKA.

